The present invention relates to a method for compensating inertia forces in the indexing movement of a machine element and an arrangement for the realization of the method.
It is customary in mechanical engineering for machine elements to be moved stepwise between predetermined positions, that is to say, to be indexed. In particular a stepwise rotation of a machine element according to a predetermined pattern is frequently used. At each rotation of the machine element at least one acceleration or deceleration occurs. Occasionally there is also an intermediate period during which the machine element is driven at constant speed. If the machine member is large, that is to say, if it has a large mass, these periodically recurring changes in speed of the machine element mean that very substantial acceleration and deceleration forces have to be applied.
On indexing (e.g. wheels of a large diameter and great mass) between different stationary positions, the inertia forces will be considerable, especially if the indexing times are short. The driving of the indexing machine element therefore requires the application of substantial forces. Even if the machine element is rotated the whole time in one direction only, shocks and vibrations arise on acceleration and deceleration of the machine element. The shocks and vibrations in addition to causing noise may also bring about damage to motor, driving unit and the machine as a whole. The result will be that the driving machine components have to be constructed for a maximum stress which occurs only during a short portion of the total working time, thus making the machine unnecessarily expensive.
Since indexing driving of machine elements is customary in mechanical engineering, it is a desirable object in general to provide a method which eliminates the problem described and which makes it possible to use smaller and consequently cheaper machine elements.
This object has been achieved in accordance with the present invention in that a method for the compensating of inertia forces during indexing movements has been given the characteristic that the machine element is connected to a cam disc against which a spring-loaded cam follower is pressed. The force of the cam follower is such that the cam disc is decelerated during the indexing movement when the cam follower is moved by the cam disc in the direction against the effect of the spring and is accelerated when the cam follower moves with the effect of the spring.
A preferred embodiment of the method in accordance with the invention has been given the further characteristic that the cam follower, via the cam disc, accelerates or decelerates the machine element as the case may be, so that its speed in the one end position of the cam follower is zero and in the other end position the speed of the cam follower is a maximum.
A further embodiment of the method in accordance with the invention has been given the further characteristic that on standstill of the cam disc the cam follower is moved to the one end position.
It is a further object of the present invention to provide an arrangement for the realization of the method. The arrangement by absorbing, storing and delivering energy provides a reduction and smoothing out of the applied driving force required, and consequently also a reduction of the vibrations occurring during the driving.
It is a further object of the present invention to provide an arrangement for the realization of the method which arrangement is simple and uncomplicated.
These and other objects have been achieved in accordance with the invention in that an arrangement for the realization of the method relating to the indexing movement of a machine element has been given the characteristic that the machine element is connected to a cam disc against which rests a spring-loaded cam follower. The shape of the cam disc is such that the cam follower during the movement of the machine element from standstill first accelerates and then decelerates the cam disc.
A preferred embodiment of the arrangement in accordance with the invention has been given the further characteristic that the cam disc has cam peaks which are situated so that the cam follower at each stop of movement is urged against the effect of the spring force into an end position in contact with one cam peak.
A further embodiment of the arrangement in accordance with the invention has been given the further characteristic that on a cam disc of the radial type the cam follower is acted on by the spring in the direction towards the axis of rotation of the cam.
A further embodiment of the arrangement in accordance with the invention has been given the further characteristic that the cam follower is in the form of a pivotably supported lever rod, one end of which rests via intermediate rolling elements against the cam disc and the other end of which is connected via a spring element to the machine frame.
A further embodiment of the arrangement in accordance with the invention has been given the further characteristic that the spring element is an air cylinder.
A further embodiment of the arrangement in accordance with the invention has been given the further characteristic that it is provided with two cam followers which rest against the cam at a spacing of 180.degree..
A further embodiment of the arrangement in accordance with the invention has been given the further characteristic that the number of cam peaks is equal to the number of stops of movement per full revolution of the cam disc.